building a cast concrete fire pit

[bobby1017]

As part of my new patio project (need to update that thread) I want a gas fire pit. I've seen some really nice concrete ones but they cost approx $2500 / 3000 for something I like. We have a machine / sheet-metal shop so I thought I could make a mold from steel, pour the concrete, then have the top surface polished. It will be 45" dia with a 32" inner bowl for a 30" high cap burner that can produce 300,000 btu, it will be manual ignition.The height is 24". Here is the burner I plan on using.

http://www.ebay.com/itm/30-SS-FIRE-PIT- ... 589438180f.

The mold will bolt together and is made from 10 ga steel, it takes 2ea) 48" x 120" sheets to produce the pieces in the laser, they will then be formed to the cone shape, have some parts welded on, then bolt to create the female form. The mold is designed, just waiting for the time to cut it.This will be able to be used multiple times if it works. I plan on having glass / ??? poured into the top of the mold so when it is polished there will be a color in the surface. The outside could be polished or some other finish, still debating. I'm not sure if this will need reinforcement (re-bar) or maybe fiber of some kind, also what size aggregate I should use. Anyone who knows about concrete could give me some info if possible.

 

[bobby1017]

Here sre the layouts for the form parts.

 

[Flippy]

Sounds cool. Post some pics. I am very interested in what it looks like in the end.

 

[bobby1017]

Initial estimate for the weight is 2000#!! That's more than I thought so I may make the inner cavity larger then I can fill with gravel after the pit is in place.

 

[bobby1017]

Still considering this but there is a lot to to it. The weight is excessive so I changed the design to be two concentric cones with about an 8" thick wall section so the outer cone is 48" dia and the inner is 32", this will get the weight in the 800# range. I have the burner parts figured out but am waiting to order until I know I can make the pit. I'm looking at a 30" high capacity burner that could produce roughly 300,000 btu, I wanted to get tall flames at times. It sure would be easy to just pay the $5000 for the one that I am modeling this after.